1. Field of the Invention
The present invention relates to an image forming apparatus and a scanning unit, and more particularly, to an image forming apparatus equipped with a scanning unit which scans and exposes the surface of a photosensitive member by means of emitting a light beam, as well as to a scanning unit provided in the image forming apparatus.
2. Description of the Related Art
An electrophotographic image-forming apparatus, such as a laser printer, forms an image by means of: deflecting a light beam emitted from a light-emitting section including a light source, such as a semiconductor laser or the like, by a deflector such as an polygon mirror; scanning and exposing a uniformly-charged surface of the photosensitive member to thus form a latent image; rendering the latent image visible with toner; and transferring a toner image on a recording medium, such as a recording sheet or the like.
A scanning apparatus that exposes and scans the surface of the photosensitive member by emitting a light beam requires highly accurate assembly in relation to the light-emitting position of a light source such as a semiconductor laser, the position of a polygon mirror, and the position of a scanning optical system, or the like, which guides a light beam to a photosensitive member.
As described in, e.g., JP-A-2004-163463 (see FIG. 1), when a conventional scanning unit is mounted on an image forming apparatus, a rigid-body plate, such as a steel plate, is usually disposed above a process unit equipped with a photosensitive drum or the like, in a direction orthogonal to the paper transport direction, to thus place the scanning unit above the rigid-body plate. In many cases, the light beam deflected by the deflector, such as a polygon mirror, is reflected by three return mirrors and guided to the surface of the photosensitive member.